Merge lp:~sil2100/ubuntu-cdimage/checksum-mtime-only into lp:ubuntu-cdimage

[Łukasz Zemczak]

Only use st.st_mtime as the entry time for checksum entries, allowing re-use of checksums for file copies and hard-links.

Only use st.st_mtime as the entry time for checksum entries, allowing re-use of checksums for file copies and hard-links.

More details on the attached bug. Quoting my comment there:
"I'd like to know if we're actually using the olddirs functionality right now, other than for removing old releases. Once we know that, I would propose using only st.st_mtime for the timestamp check. Checksums only care about the *contents* of the image, not the metadata. Move and link operations will only touch the st_ctime timestamp, so it would allow re-using the checksums in cases of image moves. Also, image moves and hard-links should be fairly safe."

In other words, I'd like to propose this change in case we don't really use the current olddirs anywhere else, as I wouldn't want to cause a regression somewhere unwillingly.

[Steve Langasek (vorlon)]

review: Approve

=== modified file 'lib/cdimage/checksums.py'
--- lib/cdimage/checksums.py	2015-10-26 11:06:11 +0000
+++ lib/cdimage/checksums.py	2019-02-12 11:54:10 +0000
@@ -83,7 +83,7 @@
     def _entry_time(self, path, default):
         try:
             st = os.lstat(path)
-            return max(st.st_mtime, st.st_ctime)
+            return st.st_mtime
         except OSError:
             return default